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Subarachnoid haemorrhage
Definition Haemorrhage into the subarachnoid space between the pia and arachnoid membranes. Clinical presentation Sudden “worst ever” headache. May have reduced GCS and may have neurological findings. Pathology '' * Where it occurs'' Berry aneurysm are saccular true aneurysm that tend to occur at branch points within or near the Circle of Willis. Thought to be due to the altered flow dynamics and areas of wall weakening at these sites. They are relatively common being found in 2-5% of the population. 20-30% have multiple aneurysms. They are more common in females. There is a weak familial risk. They are associated with various connective tissue diseases especially adult polycystic kidney disease. Smoking is also a risk factor for aneurysmal SAH. Where it Occurs At the common sites of Berry aneurysms but haemorrhage will spread widely through the subarachnoid space and into ventricles with time. Most common sites are anterior communicating artery, posterior aspect of terminal ICA either related to posterior communication artery or anterior choroidal artery, middle cerebral artery bifurcation, basilar tip and PICA origin from vertebral artery. Predominant site of haemorrhage may give clue to site of aneurysm or in the case of multiple aneurysms which one bleed. '' * Complications'' Associated intraparenchymal haemorrhage, rebleed, hydrocephalus, cerebral vasospasm. '' * Differential diagnosis'' Pseudosubarachnoid hemorrhage due to cerebral edema effacing basal cisterns, Normal structures such as calcified choroid plexus extending through foramen of Lushka, Traumatic SAH, Vascular causes other than Berry aneurysm rupture such as intradural vertebral dissection or AVM, Benign perimesencephalic haemorrhage (diagnosis of exclusion, should have typical history and benign clinical course, low pressure bleed anterior to brainstem usually limited by Lilliquist’s membrane). Radiology '' * Modality/Technique'' CT Brain C-, CT angiography, Conventional Angiography. '' * Associated conditions'' '' * Features'' High attenuation acute haemorrhage within the basal subarachnoid cisterns. Small or subtle haemorrhages may only be seen in dependent areas such as interpeduncular cistern or occipital horns of lateral ventricles. Also evaluate posterior fossa carefully which often suffers from beam hardening artefact. Look for asymmetry in lateral and Sylvian fissures. '' * Artefacts'' Beam hardening artefact. '' * Clinical Impacts'' '' * Sensitivity/specificity'' Sensitivity is very good early after the onset of symptoms but will reduce will time after this and also depends on the volume of bleed. Patients suspected of having a SAH with a negative CT should have a lumber puncture looking for xanthochromia. Management plan & communications 1) Diagnose SAH on CT. 2) Look for complications such as hydrocephalus and if the presentation has been delayed ischemia from vasospasm. 3) Perform a CT angiogram trying to optimise image quality and ensure good coverage of the most likely source of hemorrhage e.g. scan higher if you think there might be a pericallosal aneurysm. 4) Contact the clinical / neurosurgical team. 5) Look for and assess the aneurysm that caused the haemorrhage but don’t be satisfied with that, look for the 2nd or 3rd aneurysm. Is there any obvious vasospasm on the CTA? Relevant anatomy Cerebral arterial vasculature especially Circle of Willis, Normal cerebral structures that can mimic haemorrhage through physiologic calcification for example. Further reading